A variety of electrical control systems for keeping animals or excluding those animals from a designated area have long been known. The simplest of those systems comprise electrified fences, most frequently used to control cattle and keep them in a confined area. In a system of that kind, if an animal touches the electrified fence it receives a mild shock, sufficient to turn the animal back into the designated area.
Somewhat similar systems have been applied to pets, including dogs, cats, and other relatively mobile animals. Pets can be controlled by an electrified fence. More frequently, however, the pet is equipped with a collar containing a radio- frequency receiver that is activated by an electromagnetic field radiated from an antenna that encompasses the designated area in which it is desired to keep the pet. Usually, such a radio-frequency antenna has a very limited range because interference with radio reception, television reception, and the like is not permissible. With pets, the system may be reversed and may be employed to keep the pet from entering a particular area instead of confining the pet to such an area. Most pets are considerably more intelligent than cattle and other farm animals. After a few mild shocks or other alarms produced when the pet approaches a perimeter that should not be passed, the pet will shy away from that perimeter even though the radio-frequency field may no longer be present. On the other hand, the very intelligence that makes pets trainable can sometimes work to the disadvantage of the pet owner; the pet may work out a way to avoid the confining or excluding RF field. Many prior art systems are quite unsuitable for use indoors, particularly in environments in which children may also be present.
A principal problem presented in most pet training systems that employ radio-frequency fields has to do with the distance from the antenna at which the electromagnetic radiated field is effective. The ideal antenna is a single conductive wire, encompassing the area to which a pet should be confined or from which a pet should be excluded. At acceptable energizing currents for the antenna, however, usually no more than one ampere, the effective coverage or scope of the radio-frequency field may be as low as 3 inches, about 7.5 cms. If the pet is relatively young and tends to move rapidly, this means that the pet may approach and even pass the antenna wire. Of course, the pet receives a shock or is subjected to some other kind of alarm as it passes the antenna, but this does not confine the pet to a particular area nor is it effective to exclude the pet from a designated area. To be truly effective, the radiated RF electromagnetic field from the antenna should extend outwardly from the antenna for a distance, in all directions, of at least about 10 inches (25 cms) or, even better, 16 to 20 inches (40 to 50 cms). In this way, the warning or training system applies a shock or other alarm to the pet while the pet is still moving toward the antenna and before the pet can pass the antenna. For training purposes, an arrangement of this kind is much preferable.